I. Field of the Invention
This invention relates to a maleimide resin composition, as well as to a prepreg and a fiber-reinforced plastic prepared therefrom.
II. Description of the Related Art
Maleimide resin compositions are widely used in various industrial fields such as the fields of molded articles, laminated articles and adhesives by virtue of their excellent mechanical properties, chemical resistance and thermal resistance. In particular, maleimide resin compositions are widely used for fiber-reinforced composite materials containing reinforcing fibers and matrix resins as indispensable constituents. However, maleimide resin compositions have a drawback in that they are brittle, so that the cured materials thereof have low impact resistance. Especially, when a material is used as a structural material of aircraft, the low impact resistance is a serious problem.
To overcome this drawback of the maleimide resin compositions, various proposals have been made.
For example, it has been proposed to add a carboxy group-terminated butadiene-acrylonitrile rubber to the maleimide resin composition (International Adhesion and Adhesives, Vol. 5, No. 3 (1985)). However, by this method, although the toughness is promoted, the modulus of elasticity is largely decreased.
It has also been proposed to add to the maleimide resin polybenzimidazole particles (Abstract of 33rd International SAMPE Symposium); to add allylphenol having two benzene nuclei (U.S. Pat. No. 4,100,140; Japanese Patent Publication (Kokoku) No. 55-39242); to add an alkenyl-terminated aromatic oligomer (32nd International SAMPE Symposium; Japanese Laid-Open Patent Application (Kokai) No. 63-189410), or to add an aromatic oligomer such as polysulfone or polyetherketone (Japanese Laid-Open Patent Application (Kokai) No. 63-33423). However, with this methods, the improvement in the toughness is unsatisfactorily small.
Stenzenberger et al disclosed that the toughness is improved by adding a thermoplastic resin such as polyethersulfone, polyetherimide or polyhydantoin to the maleimide resin (Abstract of 33rd International SAMPE Symposium). However, with this method, although the toughness is improved, since the viscosity of the resin composition is increased by the addition of the thermoplastic resin, the moldability of the resin composition is largely reduced.
European Patent Publication No. 311,349 (1989) discloses to add an amine-terminated polyarylsulfone to the maleimide resin. The resulting maleimide resin composition gives a plastic having a homogeneous single phase structure; a plastic in which the polyarylsulfone phase and the maleimide resin phase are separated and both phases are continuous; or a plastic in which the polyarylsulfone constitutes a continuous phase and the maleimide constitutes dispersed phase, depending on the skeleton structure of the polyarylsulfone. It is also disclosed that the highest toughness is attained when both the polyarylsulfone phase and the maleimide resin phase are continuous. However, with this method, the thermal resistance of the maleimide resin is somewhat reduced.
Thus, in the prior art, the high toughness of the cured maleimide resin can only be attained at the sacrifice of elastic modulus, moldability or thermal resistance.